This invention relates to friend-or-foe identification systems (IFF), and more particularly, to a beam steered laser IFF system for use in battlefield environments.
With the advent of modern warfare, a battlefield is obviously a very dangerous place. Unfortunately, this is so both for one's comrades-in-arms as well as for the enemy. Given the amount of firepower deployed in a battle zone, the constant movement of men and material, the rapidity with which tanks, personnel carriers (APC's), planes, helicopters move, and the inability to always know (regardless of the amount of effort employed) who is where, the chances of fratricidal harm being inflicted are probably higher than they have ever been. It has thus become an imperative to greatly limit, if not altogether eliminate, casualties resulting from "friendly" fire.
One way of discerning who is a friend and who is not is by use of an IFF (Identification Friend-or-Foe) system. Various IFF systems are well-known in the art. These are typically radio frequency (RF) transmission systems, and while principally associated with aircraft, the same technology is applicable to land based vehicles, or ships. Certain RF systems, known as a co-operative systems, involve transmitting an inquiry signal to an unknown object (airplane, ship, tank). If the object is a "friendly", it has some type of transponder for responding to the inquiry with an appropriate reply. Upon receipt of an appropriate reply, the object is designated as friendly. If the object does not provide the required response, it is designated a foe and may be attacked. One drawback with co-operative systems is that it is always necessary for the object under inspection to have some mechanism for responding to an interrogation. A second drawback is that while co-operative IFF systems are the most positive types of identification systems, and have been employed for a number of years in a variety of forms, they are not infallible. This is so for a number of reasons. For example, the response mechanism on the interrogated object may be inoperative. Or, because these type systems utilize codes, the code in the response mechanism may not be up-to-date. Consequently, the failure to respond to an interrogation signal cannot always be taken as an indication that the unknown object is hostile. As RF systems, they are vulnerable to jamming. Also, because of the power requirements of RF systems, they tend to be large.
A third factor which must be considered is battlefield density. Tanks, APC's, trucks, etc., have a high spatial density. In this era of the non-linear battlefield, the possibility of friendly and enemy forces being close together is very high. Consequently, in using a co-operative system, care must be taken to avoid any ambiguities in an IFF identification. A spatially selective IFF system, using current RF technology, would require a small bandwidth and a correspondingly large antenna. At the same time, the system must have hemispheric coverage; which, in turn, requires electronic or electro-mechanical beam scanning. The result would be an expensive and impractical solution.
What is required is a type of interrogation system which provides the required selectivity without use of a cumbersome scanning technique. Such a system would produce the needed area coverage, and would do so in a cost effective and space effective manner. It would also be advantageous if the system had minimum reliance on the operability, or up-to-date information, carried by any queried targets. In this regard, laser technology may be employable in IFF systems. It is known in the art, for example, to transmit a laser beam at an unknown object and have the incident beam reflected back using a retroflector. See, for example, U.S. Pat. Nos. 5,001,348 and 4,814,769. While useful, these laser techniques still do not solve the problems. The retro-reflector is a passive unit, and the laser beam directed at the target does not include intelligence to provoke a desired response.